DESCRIPTION: (Adapted from the application) The APOE gene locus harbors a major risk factor for AD; inheritance of APOE E4 increases risk while APOE E2 decreases risk in a dose-dependent manner. Recent new data suggest that both apoE isoform and amount of apoE contribute to risk. Genetic studies have shown that three polymorphisms in the promoter/transcription enhancer elements of the APOE gene are linked to AD. These polymorphisms all have the potential to influence apoE protein levels. A different line of investigation also points in the same direction: APP over-expressing mice deficient in apoE had a striking reduction in the amount of AB deposited. The applicants propose clinical, neuropathological, and transgenic animal experiments to resolve the contribution of apoE to amyloid deposition and the risk of developing AD. First, they plan to study the impact of APOE promoter/enhancer haplotype on the clinical and neuropathological phenotype of AD. They will utilize confocal microscopy and quantitative neuropathological methods to assess apoE/AB interactions. A newly described polymorphism in the apoE receptor protein, LRP, which has been linked to AD, will be similarly analyzed. Second, in parallel with these clinical-pathological studies of AD, the applicants plan to develop a model of APP over-expression in apoE null transgenic mice in order to study the underlying biology of the extraordinary diminution in AB deposition. They will then reconstitute apoE synthesis by crossing with APOE E3 or APOE E4 over-expressing mice. These experiments are in order to allow for the direct exam of the role of both isoforms in AB deposition. By using lines with different levels of expression, the applicant intend also to address the hypothesis that apoE levels can impact AB deposition. Next, the applicants plan to reversibly-reconstitute apoE production in astrocytes by developing and applying to AD pathobiology novel gene transfer techniques (HSV-1 amplicon) that were originally developed for gene therapy. This is to allow for the study of temporal and local expression of apoE in an apoE null setting. In addition to the specific scientific aims, the infrastructure that will eventuate from quantitatively analyzed neuropathological material, clinical material, and transgenic models, is intended by the applicants to serve as a general resource for any investigator anywhere as new genetic risks may be uncovered.